Electroless Deposition of Palladium Nanoparticles on Graphdiyne Boosts Electrochemiluminescence.

Modulating the electronic structure of metal nanoparticles via metal-support interaction has attracted intense interest in the field of catalytic science. However, the roles of supporting substrates in regulating the catalytic properties of electrochemiluminescence (ECL) remain elusive. Here, we find that the use of graphdiyne (GDY) as the substrate for electroless deposition of Pd nanoparticles (Pd/GDY) produces the most pronounced anodic signal enhancement in luminol-dissolved oxygen (O2) ECL system as co-reactant accelerator over other carbon-based Pd composite nanomaterials. Pd/GDY exhibits electrocatalytic activity for the reduction of O2 through a four-electron pathway at approximately -0.059 V (vs Ag/AgCl) in neutral solution forming reactive oxygen species (ROS) as intermediates. The study shows that the interaction of Pd and GDY increases the amount and stability of ROS on the Pd/GDY electrode surface and promotes the reaction of ROS and luminol anion radical to generate excited luminol, which significantly boosts the luminol anodic ECL emission. Based on quenching of luminol ECL through the consumption of ROS by antioxidants, we develop a platform for the detection of intracellular antioxidants. This study provides an avenue for the development of efficient luminol ECL systems in neutral media and expands the biological application of ECL systems.

A Potentiometric Dual-Channel Microsensor Reveals that Fluctuation of H2 S is Less pH-Dependent During Spreading Depolarization in the Rat Brain.

Spreading depolarization (SD) is one of the most common neuropathologic phenomena in the nervous system, relating to numerous diseases. However, real-time monitoring the rapid chemical changes during SD to probe the molecular mechanism remains a great challenge. We develop a potentiometric dual-channel microsensor for simultaneous monitoring of H2 S and pH featuring excellent selectivity and spatiotemporal resolution. Using this microsensor we first observe real time changes of H2 S and pH in the rat brain induced by SD. This changes of H2 S are completely suppressed when the rat pre-treats with aminooxyacetic acid (AOAA), a blocker to inhibit the H2 S-producing enzyme, indicating H2 S fluctuation might be related to enzyme-dependent pathway during SD and less pH-dependent. This study provides a new perspective for studying the function of H2 S and the molecular basis of SD-associated diseases.

General In Situ Engineering of Carbon-Based Materials on Carbon Fiber for In Vivo Neurochemical Sensing.

Developing real-time, dynamic, and in situ analytical methods with high spatial and temporal resolutions is crucial for exploring biochemical processes in the brain. Although in vivo electrochemical methods based on carbon fiber (CF) microelectrodes are effective in monitoring neurochemical dynamics during physiological and pathological processes, complex post modification hinders large-scale productions and widespread neuroscience applications. Herein, we develop a general strategy for the in situ engineering of carbon-based materials to mass-produce functional CFs by introducing polydopamine to anchor zeolitic imidazolate frameworks as precursors, followed by one-step pyrolysis. This strategy demonstrates exceptional universality and design flexibility, overcoming complex post-modification procedures and avoiding the delamination of the modification layer. This simplifies the fabrication and integration of functional CF-based microelectrodes. Moreover, we design highly stable and selective H+, O2, and ascorbate microsensors and monitor the influence of CO2 exposure on the O2 content of the cerebral tissue during physiological and ischemia-reperfusion pathological processes.

Hydrogel-Coated Microelectrode Resists Protein Passivation of In Vivo Amperometric Sensors.

Passivation of electrodes caused by nonspecific adsorption of protein can dramatically reduce sensing sensitivity and accuracy, which is a great challenge for in vivo neurochemical monitoring. However, most antipassivation strategies are not suitable to carbon fiber microelectrodes (CFMEs) for in vivo measurement, and these methods also do not work on electrochemical biosensors that fix biometric elements. In this study, we demonstrate that chitosan hydrogel-coated microelectrodes can avoid the current passivation caused by protein adsorption on the surface of carbon fiber because the chitosan hydrogel prepared by local pH gradient caused by hydrogen evolution reaction has three-dimensional networks containing large amounts of water. The highly hydrophilic three-dimensional structure of hydrogel not only forms a biocompatible interface to confine enzymes but also keeps the fast mass transfer of analytes, such as dopamine, ascorbic acid, and glucose. The consistency of the precalibration and postcalibration of the prepared sensor enables in vivo amperometric detection of both electroactive species based on their redox property and electroinactive species based on the enzyme. This study provides a simple and versatile strategy to constitute an amperometric sensor interface to resist passivation of protein adsorption in a complex biological environment such as the brain.

Biodegradable Microelectrodes for Monitoring the Dynamics of Extracellular Ca2+ in Rat Brain.

In vivo electrochemical analysis is of great significance in understanding the dynamics of various physiological and pathological activities. However, the conventional microelectrodes for electrochemical analysis are rigid and permanent, which comes with increased risks for long-term implantation and secondary surgery. Here, we develop one biodegradable microelectrode for monitoring the dynamics of extracellular Ca2+ in rat brain. The biodegradable microelectrode is prepared by sputtering gold nanoparticles (AuNPs) on a wet-spun flexible poly(l-lactic acid) (PLLA) fiber for conduction and transduction and coating a Ca2+ ion-selective membrane (ISM) with a PLLA matrix on the PLLA/AuNPs fiber, forming PLLA/AuNPs/Ca2+ISME (ISME = ion-selective microelectrode). The prepared microelectrode shows excellent analytical properties including a near-Nernst linear response toward Ca2+ over the concentration range from 10 µM to 50 mM, good selectivity, and long-term stability for weeks as well as biocompatibility and biodegradability. The PLLA/AuNPs/Ca2+ISME can monitor the dynamics of extracellular Ca2+ following spreading depression induced by high potassium even if in the fourth day. This study provides a new design strategy for the biodegradable ISME and promotes the development of biodegradable microelectrodes for long-term monitoring of chemical signals in brain.

Biocompatible Microelectrode for In Vivo Sensing with Improved Performance.

In vivo sensing based on implantable microelectrodes has been widely used to monitor neurochemicals due to its high spatial and temporal resolution and engineering interface designability, which has become a powerful drive to decode the mysteries of degenerative diseases and regulate neural activity. Over the past few decades, with the development of a variety of advanced materials and technologies, encouraging progress has been made in quantifying various neurochemical transients. However, because of the complex chemical atmosphere including thousands of small and large biomolecules and the inherent low mechanical property of brain tissue, the design of a compatible microelectrode for the in vivo electrochemical tracking of neurochemicals with high selectivity and stability still faces great challenges. This Perspective presents a brief account of recent representative progress in the rational regulation of the microelectrode interface to resolve the questions of selectivity and sensitive decrease resulting from antiprotein adsorption, and how to decrease the mechanical mismatch of an implanted electrode with that of brain tissue. Possible future research directions on further addressing the above key issues and a more biocompatible microelectrode for in vivo long-time electrochemical analysis are also discussed.

An Electrochemical Nanosensor for Monitoring the Dynamics of Intracellular H2 O2 Upon NADH Treatment.

Reactive oxygen species (ROS)-based therapeutic strategies play an important role in cancer treatment. However, in situ, real-time and quantitative analysis of intracellular ROS in cancer treatment for drug screening is still a challenge. Herein we report one selective hydrogen peroxide (H2 O2 ) electrochemical nanosensor, which is prepared by electrodeposition of Prussian blue (PB) and polyethylenedioxythiophene (PEDOT) onto carbon fiber nanoelectrode. With the nanosensor, we find that the level of intracellular H2 O2 increases with NADH treatment and that increase is dose-dependent to the concentration of NADH. High-dose of NADH (above 10 mM) can induce cell death and intratumoral injection of NADH is validated for inhibiting tumor growth in mice. This study highlights the potential of electrochemical nanosensor for tracking and understanding the role of H2 O2 in screening new anticancer drug.

Graphdiyne: A New Carbon Allotrope for Electrochemiluminescence.

Graphdiyne (GDY), a well-known 2D carbon allotrope, demonstrates increasing fantastic performance in various fields owing to its outstanding electronic properties. Owing to its unique properties, electrochemiluminescence (ECL) technology is one powerful tool for understanding fundamental questions and for ultrasensitive sensing and imaging. Here, we firstly find that GDY without any functionalization or treatment shows a strong ECL emission with potassium persulfate (K2 S2 O8 ) as coreactant, which is totally different with other carbon allotropes. Mechanistic study indicates that the ECL emission of GDY is generated by the surface state transition. Interestingly, ECL is generated at 705 nm in the near infrared region with an ECL efficiency of 424 % compared to that of Ru(bpy)3 Cl2 /K2 S2 O8 . The study demonstrates a new character of GDY in ECL investigation and sets the stage for the development of GDY for emerging applications, including imaging and light-emitting devices.

Support-Free PEDOT:PSS Fibers as Multifunctional Microelectrodes for In Vivo Neural Recording and Modulation.

In vivo microelectrodes are essential for neuroscience studies. However, development of microelectrodes with both flexibility and multifunctionality for recording chemical and electrical signals in the same extracellular microspace and modulating neural activity remains challenging. Here, we find that pure PEDOT:PSS fibers (i.e., support-free) exhibit high conductivity, fast heterogeneous electron transfer, and suitable charge storage and injection capabilities, and can thus directly act as microelectrodes not only for chemical and electrophysiological recording in the same extracellular microspace, but also for electromodulation of neural microcircuit activity. Moreover, the microelectrodes mechanically match with neural tissues, exhibiting less foreign body responses. Given the multifunctionality, flexibility, and biocompatibility, the support-free PEDOT:PSS-based microelectrodes offer a new avenue to microelectrode technology for neuroscience research, diagnostics and therapeutics.

Vitamin D Inhibits the Early Aggregation of α-Synuclein and Modulates Exocytosis Revealed by Electrochemical Measurements.

Alpha-synuclein (α-Syn) localizes at presynaptic terminal and modulates synaptic functions. Increasing evidence demonstrate that α-Syn oligomers, forming at the early of aggregation, are cytotoxic and is thus related to brain neurodegenerative diseases. Herein, we find that vitamin D (VD) can reduce neurocytotoxicity. The reduced neurocytotoxicity might be attributed to the less amount of large-sized α-Syn oligomers inhibited by VD, measured by electrochemical collision at single particle level, which are not observable with traditionally ensembled method. Single-cell amperometry (SCA) results show that VD can recover the amount of neurotransmitter release during exocytosis induced by α-Syn oligomers, further verifying the neuroprotection of VD. Our study reveals the neuroprotective role of VD through inhibiting α-Syn aggregation, which is envisioned to be of great importance in treatment and prevention of the neurodegenerative diseases.

Synergistic Charge Percolation in Conducting Polymers Enables High-Performance In Vivo Sensing of Neurochemical and Neuroelectrical Signals.

Challenges remain in establishing a universal method to precisely tune electrochemical properties of conducting polymers for multifunctional neurosensing with high selectivity and sensitivity. Here, we demonstrate a facile and general approach to achieving synergistic charge percolation in conducting polymers (i.e., poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS) by incorporating conductive catalysts (i.e., carbon nanotubes, CNTs) and post-processing. The approach shows synergistic effects: (i) CNTs and post-processing together promote PEDOT ordered interconnection for highly efficient charge percolation that accelerates electrochemical kinetics; (ii) CNTs catalyze the electrooxidation of vitamin C for selective electrochemical sensing; (iii) CNTs enhance the charge storage/injection capacity of PEDOT:PSS. The prepared CNT-PEDOT:PSS fiber mechanically matches with neural tissues and is proved to be a biocompatible versatile microsensor capable of high-performance neurosensing in vivo.

Ag2S/Ag Nanoparticle Microelectrodes for In Vivo Potentiometric Measurement of Hydrogen Sulfide Dynamics in the Rat Brain.

Hydrogen sulfide (H2S) plays a pivotal role in gas signal transduction, neuroprotection, and regulation of physiological and pathological processes. However, in vivo tracking the dynamic of hydrogen sulfide in the complex brain environment still faces huge challenges. This study demonstrates a new potentiometric method to monitor in vivo the dynamics of hydrogen sulfide in the rat brain using silver nanoparticles (AgNPs)-modified carbon fiber microelectrodes (AgNPs/CFE) pretreated with Na2S (i.e., Ag2S/AgNPs/CFE), which acts as a solid-contact and ion-selective microelectrode. The Ag2S/AgNPs/CFE exhibits good potential response toward hydrogen sulfide in the range of 2.5-160 µM, with a detection limit of 0.8 µM. Because of the presence of Ag2S, the Ag2S/AgNPs/CFE shows good selectivity to hydrogen sulfide, avoiding the interference from coexistent electroactive neurochemicals and the analogies, such as ascorbic acid and cysteine in the central nervous system. This good selectivity combined with the reversibility, protein antifouling, and biocompatibility of the microelectrode enables the Ag2S/AgNPs/CFE to detect hydrogen sulfide in the rat brain during local microinfusion of Na2S and the change in pH. Our study provides a reliable method to track hydrogen sulfide selectively in vivo, which will help to explore the function of hydrogen sulfide in neurophysiology and pathology.

Zwitterionic Polydopamine Engineered Interface for In Vivo Sensing with High Biocompatibility.

Electrochemical sensing performance is often compromised by electrode biofouling (e.g., proteins nonspecific binding) in complex biological fluids; however, the design and construction of a robust biointerface remains a great challenge. Herein, inspired by nature, we demonstrate a robust polydopamine-engineered biointerfacing, to tailing zwitterionic molecules (i.e., sulfobetaine methacrylate, SBMA) through Michael Addition. The SBMA-PDA biointerface can resist proteins nonspecific binding in complex biological fluids while enhancing interfacial electron transfer and electrochemical stability of the electrode. In addition, this sensing interface can be integrated with tissue-implantable electrode for in vivo analysis with improved sensing performance, preserving ca. 92.0% of the initial sensitivity after 2 h of implantation in brain tissue, showing low acute neuroinflammatory responses and good stability both in normal and in Parkinson's disease (PD) rat brain tissue.

Unveiling the Role of DJ-1 Protein in Vesicular Storage and Release of Catecholamine with Nano/Micro-Tip Electrodes.

DJ-1 protein deficiency caused by PARK7 gene mutation has been suggested to closely relate to Parkinson's disease (PD), mainly through the attenuation D2 dopamine receptor activity in mice; however, whether or how it affects the vesicular storage and exocytosis of neurochemicals remains unclear. By using electrochemical methods at a single vesicle/cell level with nano/micro-tip electrodes, we for the first time find that DJ-1 protein deficiency caused by PARK7 gene knockout (KO) in mice has little effect on vesicular catecholamine content but significantly prolongs the exocytotic events, especially the closing time of exocytotic fusion pores. Further studies suggest the inhibition of α-synuclein aggregation by DJ-1 protein might be one way that DJ-1 protein acts on neurotransmission. This finding offers the first direct link between DJ-1 protein deficiency and vesicular chemical storage and release of chemicals, providing a new chemical insight into the pathology of PD caused by PARK7 gene mutation.

A Generalizable and Noncovalent Strategy for Interfacing Aptamers with a Microelectrode for the Selective Sensing of Neurotransmitters In†Vivo.

The selective sensing of neurochemicals is essential for understanding the chemical basis of brain function and pathology. Interfacing the excellent recognition features of aptamers with in vivo compatible carbon fiber microelectrode (CFE)-based electroanalytical systems offers a plausible means to achieve this end. However, this is challenging in terms of coupling chemistry, stability, and versatility. Here, we present a new interfacial functionalization strategy based on the assembly of aptamer cholesterol amphiphiles (aptCAs) on the alkyl chain-functionalized CFE. The noncovalent cholesterol-alkyl chain interactions effectively immobilize aptamers onto the CFE surface, allowing the generation of a highly selective system for probing neurochemical dynamics in living systems and opening up a vast array of new opportunities for designing in vivo sensors for exploring brain chemistry.

Nanoscale ATP-Responsive Zeolitic Imidazole Framework-90 as a General Platform for Cytosolic Protein Delivery and Genome Editing.

Metal-organic frameworks (MOFs) are an emerging class of nanocarriers for drug delivery, owing to their tunable chemical functionality. Here we report ATP-responsive zeolitic imidazole framework-90 (ZIF-90) as a general platform for cytosolic protein delivery and CRISPR/Cas9 genome editing. The self-assembly of imidazole-2-carboxaldehyde and Zn2+ with protein forms ZIF-90/protein nanoparticles and efficiently encapsulates protein. It was found that, in the presence of ATP, the ZIF-90/protein nanoparticles are degraded to release protein due to the competitive coordination between ATP and the Zn2+ of ZIF-90. Intracellular delivery studies showed that the ZIF-90/protein nanoparticle can deliver a large variety of proteins into the cytosol, regardless of protein size and molecular weight. The delivery of cytotoxic RNase A efficiently prohibits tumor cell growth, while the effective delivery of genome-editing protein Cas9 knocks out the green fluorescent protein (GFP) expression of HeLa cells with efficiency up to 35%. Given the fact that ATP is upregulated in disease cells, it is envisaged that the ATP-responsive protein delivery will open up new opportunities for an advanced protein delivery and CRISPR/Cas9 genome editing for targeted disease treatment.

Collision of Aptamer/Pt Nanoparticles Enables Label-Free Amperometric Detection of Protein in Rat Brain.

Single particle collision is emerging as a powerful and sensitive technique for analyzing small molecules, however, its application in biomacromolecules detection, for example, protein, in complex biological environments is still challenging. Here, we present the first demonstration on the single particle collision that can be developed for the detection of platelet-derived growth factor (PDGF), an important protein involved in the central nervous system in living rat brain. The system features Pt nanoparticles (PtNPs) conjugated with the PDGF recognition aptamer, suppressing the electrocatalytic collision of PtNPs toward the oxidation of hydrazine. In the presence of PDGF, the stronger binding between targeted protein and the aptamer disrupts the aptamer/PtNPs conjugates, recovering the electrocatalytic performance of PtNPs, and allowing quantitative, selective, and highly sensitive detection of PDGF in cerebrospinal fluid of rat brain.

Low-Fouling Nanoporous Conductive Polymer-Coated Microelectrode for In Vivo Monitoring of Dopamine in the Rat Brain.

In vivo electrochemistry with a carbon-fiber electrode (CFE) is the most useful method for tracking neurochemicals in specific brain regions due to its high spatiotemporal resolution. However, CFE is inevitably subject to surface biofouling that leads to a decrease in sensitivity. Here, we develop a polytannic acid (PTA)-doped nanoporous conductive polyaniline (PANI) membrane-coated CFE to minimize biofouling-induced negative effects for in vivo analysis. The as-prepared PTA-PANI-coated CFE shows excellent antifouling property and enrichment capacity toward electrochemical measurement of dopamine (DA) in physiological pH. The PTA-PANI-coated CFE can in vivo monitor the release of DA induced by electrical stimulation and exhibits almost the same sensitivity in the postcalibration (Spost) and the precalibration (Spre; Spost/Spre = 0.90). We believe this conductive nanoporous membrane-coated CFE offers a new platform for in vivo measurement, which would help probe brain chemistry.

Observing Single Hollow Porous Carbon Catalyst Collisions for Oxygen Reduction at Gold Nanoband Electrode.

The evaluation of single carbon particle catalysts is critical to better understand the relationship between structure and properties. Here, we use an electrochemical collision method to study the electrocatalytic behaviour of single hollow porous carbon catalyst on gold nanoband electrodes (AuNBE). We observed the catalytic current of oxygen reduction of single carbon particle and quantified the contribution of the porous structure to the catalytic performance. We find that the meso/microporous and hollow structures contribute to the electrocatalytic current. Our research provides direct evidence that the hollow/porous structures improve the electrocatalytic performance.

A cobalt corrole/carbon nanotube enables simultaneous electrochemical monitoring of oxygen and ascorbic acid in the rat brain.

It is of interest to in vivo monitor the co-dynamics of different substances. However, the tracking of multiple species is still challenging. In this work, we demonstrate an in vivo electrochemical method by using multi-potential step amperometry to in vivo detect ascorbic acid (AA) and oxygen (O2) simultaneously. In order to achieve good selectivity and high sensitivity for both AA and O2, we design a cobalt corrole [Co(tpfc)(py)2] (tpfc = 5,10,15-tris(penta-fluorophenyl) corrole, py = pyridine, denoted as Co-TPFC) and carbon nanotube nanocomposite to modify a carbon fiber microelectrode (Co-TPFC/MWNT/CFE). This Co-TPFC/MWNT/CFE exhibits excellent electrocatalytic properties towards the reduction of O2 preceding a 4e process and facilitates the oxidation of AA at low potential in the physiological environment. Based on this, we realize simultaneous detection of AA and O2 using two-potential steps (one cathodic (-0.2 V) and the other anodic (+0.05 V)) with 1 second step time. Both in vitro and in vivo experiments proved the feasibility of this method. This demonstrated strategy is useful for us to understand various physiological and pathological processes associated with O2 and AA co-dynamics, and also provides an idea for detecting multiple substances simultaneously.